The use of repeaters in various types of wireless communications systems (e.g., cellular and PCS) generally is known. Wireless communications systems typically include a base station and one or more fixed or mobile subscriber units.
Repeaters are bi-directional devices which relay signals from a cellular or PCS base station to the mobile or fixed subscriber units and from subscriber units to the base station. The repeater extends the base station signals to provide a stronger signal in areas which have little or no signal. The repeater includes a donor antenna, which relays signals between the repeater and the base station, and a subscriber antenna, which relays signals between the base station and the mobile or fixed subscriber units.
The operation of the repeater is based, in part, on the isolation obtained between a donor/subscriber antenna pair. The greater the isolation, the better the performance. Currently, isolation is obtained by physically separating donor and subscriber antennas either vertically or horizontally. To achieve a desired amount of isolation, a relatively substantial distance is required between the antennas. This distance requirement both increases the cost of the repeater and decreases the aesthetics of the repeater site.
Many existing repeaters use vertically polarized antennas. This approach suffers from various drawbacks including the need to physically space the antennas a relatively large distance apart to achieve an acceptable level of isolation and these systems are highly susceptible to relatively poor performance due to multipath, fading, and other factors. Multipath occurs, for example, when signals reach the same point via different paths.
Additionally, using vertical polarization often causes a relatively significant problem with hand-held antenna tilt. The vertically polarized signal received by the hand-held unit is rarely vertical due to normal transmission fluctuations. The amount of tilt of the hand-held unit varies with the particular operator and the conditions and environments prevailing. Losses from the antenna position and the received signal polarization angle mismatch can be significant (e.g., above 10 dB). Furthermore, vertical polarization is not entirely successful in eliminating interference.
These and other problems can lead to distortion, cancellation, and loss of signal strength.
These and other drawbacks exist in previously known systems.